A demonstrator holds a poster of Clement Meric during a protest rally in Paris. Photo: AFP

Politicians across the spectrum condemned the incident, with some calling for the government to ban groups they say are becoming increasingly violent and brazen in their actions.

Marine Le Pen, head of the far-right National Front, said her party had "no link" with the "horrendous" incident.

Anne Hidalgo, the Socialist candidate in next year's Paris mayoral race, condemned a "despicable act", while France's upper house Senate called it a "horrendous murder".

Left-wing parties – including France's ruling Socialists – called for people to rally in Paris on Thursday for "the dissolution of ultra-violent far-right groups".

Far-right groups have been blamed for violent clashes that marred a number of recent protests over France's legalisation of gay marriage.

The country's interior minister Manuel Valls said the tragedy "bears the marks of the far-right".

Meanwhile, President Francois Hollande sent his "support and solidarity" to the family of the victim and Prime Minister Jean-Marc Ayrault vowed to "find legal and political responses to beat racist, anti-Semitic and homophobic movements".

Reports diverge on what sparked the fight outside a shop that sold clothes popular with far-right activists and skinheads near the train station.

Police said a group of young "skinhead types" found themselves in the shop with another group that included Mr Meric, sparking a wave of insults and jostling.

The skinheads then left the shop and waited for the group outside with other people, and the victim "was hit by one of the skinheads who wore a knuckleduster and fell on the pavement, hitting a bollard".

A police source said the victim was involved in the "extreme-left anti-fascist movement".

Left-wing activists said the skinheads were part of the extreme-right Revolutionary Nationalist Youth (JNR) group.

But Serge Ayoub, the leader of the JNR, said his group was not involved in the incident, adding that the far-left activists were the ones who left the shop first and waited for the skinheads, sparking the fight.

Rallies denouncing the attack were also planned in major French cities including Marseille, Lyon, Toulouse and Lille.

On Twitter, the incident was one of the most talked about topics in France, with the name of the victim, JNR and #antifa, short for anti-fascist, all trending on the social network.